Solenoid valve

ABSTRACT

A solenoid valve includes a main valve having a valve seat and a main valve body configured to open or close a main flow passage, a pilot passage that branches from the main flow passage, an orifice provided in the pilot passage, a back-pressure chamber configured to bias the main valve body to a closing direction by virtue of an internal pressure, a pilot valve configured to control an internal pressure of the back-pressure chamber, and a solenoid configured to control a valve opening pressure of the pilot valve. There is a time difference between a valve opening timing of the main valve and a valve opening timing of the pilot valve such that the valve opening timing of the main valve is delayed from the valve opening timing of the pilot valve.

TECHNICAL FIELD

This invention relates to a solenoid valve.

BACKGROUND ART

It is known that a solenoid valve is used as a controllable damping valve capable of controlling a damping force of a shock absorber interposed between a chassis and an axle of a vehicle. In JP 2009-222136 A, there is discussed such a solenoid valve. The solenoid valve includes an annular valve seat provided in a main flow passage connected from a cylinder of the shock absorber to a reservoir, a main valve body seated on or unseated from the annular valve seat to open or close the main flow passage, a pilot passage branching from the main flow passage, an orifice provided in the pilot passage, a back-pressure chamber provided in a rear face side of the main valve body opposite to the valve seat side, a pilot valve provided in a downstream of the pilot passage, and a solenoid configured to control a valve opening pressure of the pilot valve.

A secondary pressure downstream from the orifice in the pilot passage is introduced into the back-pressure chamber, and the main valve body is pressed by the secondary pressure. Since the pilot valve is provided downstream from the back-pressure chamber, the secondary pressure introduced into the back-pressure chamber is controlled by the valve opening pressure of the pilot valve by adjusting the valve opening pressure of the pilot valve using a thrust force of the solenoid.

The secondary pressure is applied to the rear face of the main valve body to exert a force such that the main valve body is pressed toward the valve seat side. A pressure is applied from the upstream of the main flow passage to the front face of the main valve body to exert a force such that the main valve body is flexed and is unseated from the valve seat. Therefore, the main valve body is opened when the force of unseating the main valve body from the valve seat by virtue of the pressure from the upstream side of the main flow passage exceeds the force of pressing the main valve body to the valve seat by virtue of the secondary pressure.

That is, it is possible to adjust the valve opening pressure of the main valve body by controlling the secondary pressure. Therefore, the solenoid valve can change resistance to the liquid flow passing through the main flow passage by adjusting the valve opening pressure of the pilot valve using the solenoid so that a desired damping force can be generated in the shock absorber.

SUMMARY OF INVENTION

The solenoid valve of the prior art described above is provided with a spring for biasing the pilot valve to open the pilot passage. The solenoid exerts a thrust force for closing the pilot passage toward the pilot valve. That is, the valve opening pressure of the pilot valve is adjusted by changing the electric current amount applied to the solenoid.

As the pilot valve is opened, the solenoid valve releases the pressure of the upstream side of the pilot passage to the reservoir. As a result, the back-pressure chamber is controlled by the valve opening pressure of the pilot valve. However, since a delay occurs when the pilot valve is opened from the closed state, the internal pressure of the back-pressure chamber rises over the valve opening pressure of the pilot valve only for an instant. Then, as the pilot valve is opened, and the pressure is released, the pressure of the back-pressure chamber decreases to the valve opening pressure.

In this manner, since the opening level of the main flow passage of the main valve body abruptly changes due to an abrupt change of the internal pressure of the back-pressure chamber at the time of opening the pilot valve, the damping force generated by the shock absorber also abruptly changes. As a result, vibration of a chassis or abnormal noise in a cabin may be generated.

In view of the aforementioned problems, it is therefore an object of this invention to provide a solenoid valve capable of alleviating an abrupt change of the damping force.

According to one aspect of the present invention, a solenoid valve includes a main valve having a valve seat provided in a main flow passage, and a main valve body seated on or unseated from the valve seat to open or close the main flow passage, a pilot passage that branches from the main flow passage, an orifice provided in the pilot passage, a back-pressure chamber connected to the pilot passage downstream from the orifice, the back-pressure chamber being configured to bias the main valve body to a closing direction by virtue of an internal pressure, a pilot valve disposed in the pilot passage downstream from a connection point to the back-pressure chamber, the pilot valve being configured to control an internal pressure of the back-pressure chamber, and a solenoid configured to control a valve opening pressure of the pilot valve. There is a time difference between a valve opening timing of the main valve and a valve opening timing of the pilot valve such that the valve opening timing of the main valve is delayed from the valve opening timing of the pilot valve.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a solenoid valve according to a first embodiment of this invention;

FIG. 2 is a cross-sectional view illustrating a shock absorber provided with the solenoid valve of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a relationship between a front-side pressure receiving area and a rear-side pressure receiving area of the main valve body; and.

FIG. 4 is a diagram illustrating a relationship between the electric current supplied to the solenoid and the damping force of the shock absorber provided with the solenoid valve.

DESCRIPTION OF EMBODIMENTS

A description will now be made for embodiments of this invention with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating a solenoid valve V according to this embodiment. The solenoid valve V includes a main valve M having a valve seat 2 provided in the main flow passage 1 and an annular leaf valve 3 seated on or unseated from the valve seat 2 to serve as a main valve body for opening or closing the main flow passage 1, a pilot passage 4 branching from the main flow passage 1, an orifice 5 provided in the pilot passage 4, a back-pressure chamber P connected to the pilot passage 4 downstream from the orifice 5 to bias the leaf valve 3 to a closing direction using an internal pressure, a pilot valve 6 disposed in the pilot passage 4 downstream from a connection point to the back-pressure chamber P to control an internal pressure of the back-pressure chamber P, a solenoid Sol configured to adjust the valve opening pressure of the pilot valve 6. The solenoid valve V is applied to a shock absorber D.

FIG. 2 is a cross-sectional view illustrating a shock absorber provided with the solenoid valve V of FIG. 1. The shock absorber D usually generates a damping force by applying resistance to a fluid passing through the main flow passage 1 in the event of expansion or contraction.

The shock absorber D includes a cylinder 10, a piston 11 slidably inserted into the cylinder 10, a rod 12 movably inserted into the cylinder 10 and connected to the piston 11, a rod-side chamber 13 and a piston-side chamber 14 partitioned by the piston 11 inside the cylinder 10, a pipe 16 that covers the outer circumference of the cylinder 10 to form a discharge passage 15 with the cylinder 10, and an outer tube 18 that covers the outer circumference of the pipe 16 to form a reservoir 17 with the pipe 16.

Hydraulic oil as a fluid is filled in the rod-side chamber 13, the piston-side chamber 14, and the reservoir 17 while the reservoir 17 is filled with gas in addition to the hydraulic oil. It is noted that the fluid may include any material other than the hydraulic oil if it can exert a damping force.

The shock absorber D further includes an inlet passage 19 that allows only for a flow of the hydraulic oil directed from the reservoir 17 to the piston-side chamber 14, and a piston passage 20 provided in the piston 11 to allow only for a flow of the hydraulic oil directed from the piston-side chamber 14 to the rod-side chamber 13. The discharge passage 15 causes the rod-side chamber 13 and the reservoir 17 to communicate with each other. The solenoid valve V is provided in the discharge passage 15 such that the main flow passage 1 is connected to the discharge passage 15 (FIG. 1).

When the shock absorber D is operated to contract, the piston 11 moves downward in FIG. 2 so that the piston-side chamber 14 is compressed, and the hydraulic oil of the piston-side chamber 14 moves to the rod-side chamber 13 via the piston passage 20. During the contraction, since the rod 12 intrudes into the cylinder 10, the amount of the hydraulic oil becomes excessive as much as the rod intrudes into the cylinder 10. Therefore, the excessive hydraulic oil is extruded from the cylinder 10 and is discharged to the reservoir 17 via the discharge passage 15. Since the shock absorber D applies resistance to the flow of the hydraulic oil moving to the reservoir 17 via the discharge passage 15 by virtue of the solenoid valve V, the internal pressure of the cylinder 10 increases, and a contractive damping force is exerted.

When the shock absorber D is operated to expand, the piston 11 moves upward in FIG. 2, so that the rod-side chamber 13 is compressed, and the hydraulic oil of the rod-side chamber 13 moves to the reservoir 17 via the discharge passage 15. During the expansion, the piston 11 moves upward, and the volume of the piston-side chamber 14 increases. Therefore, the hydraulic oil is supplied from the reservoir 17 via the inlet passage 19 as much as the volume increases. Since the shock absorber D applies resistance to the flow of the hydraulic oil moving to the reservoir 17 via the discharge passage 15 by virtue of the solenoid valve V, the internal pressure of the rod-side chamber 13 increases, and an expansive damping force is exerted.

When the shock absorber D is operated to expand or contract, the hydraulic oil is necessarily discharged from the cylinder 10 to the reservoir 17 via the discharge passage 15. That is, the shock absorber D is a uni-flow type shock absorber in which the hydraulic oil is circulated in a unidirectional manner in the order of the piston-side chamber 14, the rod-side chamber 13, and the reservoir 17 and generates both expansive and contractive damping forces by virtue of a single solenoid valve V.

It is noted that, if the cross-sectional area of the rod 12 is set to a half of the cross-sectional area of the piston 11, the amount of the hydraulic oil discharged from the cylinder 10 can be set to be the same between expansion and contraction with the same amplitude. Therefore, if the resistance to the flow caused by the solenoid valve V becomes constant, it is possible to set the expansive and contractive damping forces to the same value.

The solenoid valve V includes a seat member 21 that is fitted to a sleeve 16 a provided in an opening of the pipe 16 and has a main flow passage 1, an annular valve seat 2, and an orifice 5, a leaf valve 3 mounted to an outer circumference of the seat member 21 and seated on or unseated from the valve seat 2 to serve as a main valve body, a valve housing 22 connected to the seat member 21 to form a cavity, a pilot valve 6 inserted into the valve housing 22 movably along an axial direction, a solenoid Sol that exerts a thrust force to the pilot valve body 38 in the pilot valve 6, and a main spool 23 that is slidably mounted to an outer circumference of the valve housing 22 and abuts on the rear face of the leaf valve 3 (the right face of FIG. 1) to define the back-pressure chamber P in the rear face side of the leaf valve 3. The pilot passage 4 is formed in the seat member 21 and the inside of the valve housing 2.

The seat member 21 includes a large-diameter basal portion 21 a fitted to the sleeve 16 a, a shaft portion 21 b protruding to the right side of FIG. 1 from the basal portion 21 a, a cavity 21 c formed to penetrate through the basal portion 21 a and the shaft portion 21 b in an axial direction to form a part of the pilot passage 4, a penetrating hole 21 d opened on the outer circumference of the shaft portion 21 b to communicate with the cavity 21 c, an orifice 5 provided in the discharge passage 15 side upstream from the connection point of the penetrating hole 21 d in the cavity 21 c, a main flow passage 1 provided with a plurality of ports perforating through the basal portion 21 a from the left end to the right end of FIG. 1, and an annular valve seat 2 provided in an exit of the main flow passage 1 which is the right end of the basal portion 21 a in FIG. 1.

The main flow passage 1 penetrates through the basal portion 21 a. The opening of the main flow passage 1 provided in the left end side of the basal portion 21 a in FIG. 1 communicates with the rod-side chamber 13 via the discharge passage 15 formed with the pipe 16. The opening of the main flow passage 1 in the right end side of the basal portion 21 a in FIG. 1 communicates with the reservoir 17. Similar to the main flow passage 1, the opening of the cavity 21 c in the left end side of FIG. 1 communicates with the rod-side chamber 13 via the discharge passage 15.

In addition, a window 21 e formed as an annular groove causing each port of the main flow passage 1 to communicate with each other is provided in the right end of the basal portion 21 a in FIG. 1. The outer circumference of the window 21 e is surrounded by the valve seat 2. The inner circumference of the window 21 e is provided with an inner circumferential seat portion 21 f.

It is noted that a seal ring 24 is mounted to an outer circumference of the basal portion 21 a of the seat member 21. As a result, a gap between the outer circumference of the basal portion 21 a and the inner circumference of the sleeve 16 a is sealed, so that the discharge passage 15 is prevented from communicating with the reservoir 17 via the outer circumference of the basal portion 21 a.

In the right end of the basal portion 21 a of the seat member 21 in FIG. 1, the annular leaf valve 3 seated on or unseated from the valve seat 2 to open or close the main flow passage 1 is stacked. The valve seat 2 and the leaf valve 3 constitute a main valve M. The inner circumference of the leaf valve 3 is interposed between the inner circumferential seat portion 21 f and the valve housing 22 and is fixed to the outer circumference of the shaft portion 21 b. Therefore, the outer circumference of the leaf valve 3 can be flexed as a free end. As the leaf valve 3 is flexed by receiving a pressure applied to the front face (the left face in FIG. 1) from the upstream of the main flow passage 1, the leaf valve 3 is unseated from the valve seat 2 to open the main flow passage 1. It is noted that the leaf valve 3 is a layered leaf valve obtained by stacking a plurality of annular sheets, and the number of the annular sheets may be arbitrarily set. In addition, a cutout orifice 3 a is provided in the outer circumference of the annular sheet seated on the valve seat 2.

As illustrated in FIG. 3, a front face-side pressure receiving area As which is an area of the face of the leaf valve 3 receiving a pressure of the upstream of the main flow passage 1 corresponds to an area of the portion of the leaf valve 3 facing the window 21 e between the valve seat 2 and the inner circumferential seat portion 21 f. The front face-side pressure receiving area As may be set to an arbitrary size by changing a diameter (seat diameter) of the inner circumference of the cross-sectional area of the valve seat 2 making contact with the leaf valve 3. Similarly, the front face-side pressure receiving area As may change by changing a diameter of the outer circumference of the cross-sectional area of the inner circumferential seat portion 21 f making contact with the leaf valve 3.

The valve housing 22 having a tubular shape has an annular pilot valve seat 22 a formed as a small diameter portion provided in the center inner circumference. The valve housing 22 is connected to the seat member 21 by inserting and screwing the shaft portion 21 b of the seat member 21 into the left side from the pilot valve seat 22 a in FIG. 1. As a result, the inner circumference of the leaf valve 3 is interposed between the basal portion 21 a of the seat member 21 and the left end of the valve housing 22 in FIG. 1. It is noted that the outer diameter of the valve housing 22 in the left end of FIG. 1 is formed to have a small diameter not to hinder the leaf valve 3 from being flexed.

The inner diameter of the left-end opening of the valve housing 22 in FIG. 1 is larger than the diameter of the portion where the shaft portion 21 b is screwed. An annular gap R is formed between the seat member 21 and the valve housing 22 when the shaft portion 21 b of the seat member 21 is inserted. In the left end of the valve housing 22 of FIG. 1, a cutout trench 22 e extending in a radial direction is provided, so that the outer circumferential side of the valve housing 22 communicates with the annular gap R via the cutout trench 22 e when the left end of the valve housing 22 abuts on the leaf valve 3. The annular gap R also communicates with the penetrating hole 21 d formed in the shaft portion 21 b of the seat member 21. It is noted that, although the cutout trench 22 e is a trench formed in the left end of the valve housing 22 in FIG. 1, any other configuration such as a hole penetrating through the valve housing 22 may also be possible instead.

The valve housing 22 is provided with a flange 22 b in the outer circumference. The flange 22 b is fitted to the inner circumference of the tube 18 b provided in the opening 18 a formed in the lateral side of the outer tube 18 and abuts on the step portion 18 c provided in the inner circumference of the tube 18 b. It is noted that the tube 18 b is provided with a thread portion (not illustrated) in the outer circumference of the edge. A bottomed tubular casing 25 including the solenoid Sol is screwed to the tube 18 b. As the casing 25 is screwed to the tube 18 b, the flange 22 b of the valve housing 22 is fixed to the tube 18 b, and the seat member 21 screwed to the valve housing 22 is also fixed to a predetermined position of the tube 18 b.

It is noted that a gap between the sleeve 16 a and the seat member 21 is sealed by the seal ring 24 mounted in the outer circumference of the seat member 21, so that the basal portion 21 a of the seat member 21 is inserted into the sleeve 16 a with a margin. As a result, even when there is a deviation of the axial center between the tube 18 a and the sleeve 16 a, it is possible to easily fit the flange 22 b of the valve housing 22 into the tube 18 b.

The valve housing 22 has a through-hole 22 c provided in a radial direction in the right side of FIG. 1 from the flange 22 b and the pilot valve seat 22 a to cause the inside and the outside to communicate with each other. The outer circumference of the valve housing 22 in the right side of FIG. 1 from the through-hole 22 c is provided with a flange-like sliding contact portion 22 d where a failsafe valve body 42 of a tubular failsafe valve 26 is slidably mounted. The flange 22 b is provided with a through-hole 22 f penetrating in the axial direction so that the space of the right side of FIG. 1 from the flange 22 b communicates with the reservoir 17 of the left side.

The inside of the valve housing 22 communicates with the discharge passage 15 via the cavity 21 c provided in the seat member 21 and with the rod-side chamber 13 via the discharge passage 15. The inside of the valve housing 22 communicates with the reservoir 17 via the through-holes 22 c and 22 f. That is, the valve housing 22 forms the pilot passage 4 branching from the main flow passage 1 and causing the rod-side chamber 13 and the reservoir 17 to communicate with each other in combination with the cavity 21 c of the seat member 21.

A tubular main spool 23 having a brim 23 a in its outer circumference is slidably mounted to the outer circumference of the valve housing 22 in the left side of FIG. 1 from the flange 22 b. A spring 27 serving as a biasing mechanism is interposed between the brim 23 a of the main spool 23 and the flange 22 b. The spring 27 biases the main spool 23 toward the leaf valve 3 in the left side of FIG. 1 and causes the main spool 23 to abut on the right face of FIG. 1 (the rear face of the leaf valve 3). It is noted that the biasing mechanism may include various springs such as a coil spring or a disc spring or an elastic body such as rubber capable of exerting a resilient force against compression.

While the main spool 23 abuts on the rear face of the leaf valve 3, the back-pressure chamber P is defined in the rear face of the leaf valve 3 by virtue of the main spool 23. The back-pressure chamber P communicates with the cavity 21 c of the pilot passage 4 via the cutout trench 22 e, the annular gap R, and the penetrating hole 21 d described above. The cutout trench 22 e, the annular gap R, and the penetrating hole 21 d constitute a communication passage Pr. The internal pressure of the pilot passage 4 propagates to the back-pressure chamber P via the communication passage Pr.

The back-pressure chamber P is an annular space between the outer circumference of the valve housing 22 and the main spool 23 and applies its internal pressure to the rear face of the leaf valve 3. A rear face-side pressure receiving area Ah which is an area of the face of the leaf valve 3 where the internal pressure is applied corresponds to an area of the portion of the rear face of the leaf valve 3 facing the back-pressure chamber P. The rear face-side pressure receiving area Ah is an area of the annular surface obtained by cutting away the inner edge of the end surface of the main spool 23 making contact with the leaf valve 3 and the outer edge of the end surface of the valve housing 22 making contact with the leaf valve 3. The rear face-side pressure receiving area Ah can be set to an arbitrary size by changing an inner diameter of the end surface of the main spool 23 making contact with the leaf valve 3. Similarly, the rear face-side pressure receiving area Ah may change by changing an outer diameter of the end surface of the valve housing 22 making contact with the leaf valve 3.

The annular gap R is provided to cause the penetrating hole 21 d and the cutout trench 22 e to reliably communicate with each other even when the penetrating hole 21 d and the cutout trench 22 e do not face each other in the radial direction. However, the annular gap R may be omitted if the penetrating hole 21 d and the cutout trench 22 e face each other in the radial direction.

The internal pressure of the back-pressure chamber P is also applied to the rear face of the leaf valve 3 in addition to the biasing force for biasing the main spool 23 from the spring 27, so that the leaf valve 3 is biased toward the valve seat 2. That is, when the shock absorber D is operated to expand or contract, the internal pressure of the rod-side chamber 13 is applied to the leaf valve 3 from the front face side via the main flow passage 1, so that both the internal pressure of the back-pressure chamber P and the biasing force of the spring 27 are applied to the leaf valve 3 from the rear face side.

In this case, the force applied to the front side of the leaf valve 3 to flex the outer circumference of the leaf valve 3 to the right side of FIG. 1 is a force obtained by multiplying the front face-side pressure receiving area As by the internal pressure of the rod-side chamber 13. If this force exceeds a sum of flexural rigidity of the leaf valve 3, the force obtained by multiplying the internal pressure of the back-pressure chamber P by the rear face-side pressure receiving area Ah of the rear face of the leaf valve 3, and the biasing force of the spring 27, the spring 27 is compressed, the main spool 23 retreats from the basal portion 21 a, and the leaf valve 3 is flexed, so that the main flow passage 1 is opened.

The casing 25 includes a tubular portion 25 a, a bottom portion 25 b caulked to the opening end of the tubular portion 25 a, and an annular stopper 25 c fixed to the inner circumference side of the tubular portion 25 a to hold a solenoid bobbin 29 where the coil 28 of the solenoid Sol is wound. The flange 22 b of the valve housing 22 and a nonmagnetic spacer 35 are interposed using the stopper 25 c and the step portion 18 c of the tube 18 b. As a result, the valve housing 22 and the seat member 21 are fixed to the shock absorber D. It is noted that, since the flange 22 b is provided with a through-hole 22 f, the pilot passage 4 and the reservoir 17 remain to communicate with each other.

The solenoid Sol includes a casing 25 having a bottomed tubular shape, an annular solenoid bobbin 29 fixed to the bottom of the casing 25, where coil 28 is wound, a first stator 30 that has a bottomed tubular shape and is fitted to the inner circumference of the solenoid bobbin 29, a second stator 31 that has a tubular shape and is fitted to the inner circumference of the solenoid bobbin 29, a nonmagnetic ring 32 fitted to the inner circumference of the solenoid bobbin 29 and interposed between the first and second stators 30 and 31, a rotor 33 that has a bottomed tubular shape and is disposed in the inner circumferential side of the first stator 30, and a tubular failsafe valve 26 slidably mounted to the outer circumference of the sliding contact portion 22 d of the valve housing 22 to serve as a rotor as well.

An opening end side of the rotor 33 having a bottomed tubular shape is slidably inserted into the inner circumference of the first stator 30 to face the inside of the first stator 30. The dimension of the rotor 33 is set such that the bottom side face in the left side of FIG. 1 faces or is arranged in the vicinity of the inner circumference of the second stator 31 even when it enters the inside of the first stator 30 until it abuts on a nonmagnetic washer 34 provided in the bottom of the first stator 30. The tube of the rotor 33 is provided with a communication hole 33 a formed in an axial direction, and the spaces partitioned by the first stator 30 and the rotor 33 communicate with each other via the communication hole 33 a.

A spring 36 is interposed between the rotor 33 and the first stator 30. The rotor 33 receives a thrust force from the spring 36 to retreat from the first stator 30. The spring 36 is supported by a spring bearing 37 a provided in a leading end of a spring force adjustment screw 37 whose right end of FIG. 1 is screwed to the axial core of the first stator 30. The support position of the spring 36 may change across the left and right sides of FIG. 1 by advancing or retreating the spring force adjustment screw 37 against the first stator 30. It is noted that, according to this embodiment, manipulation of the spring force adjustment screw 37 is prohibited after the bottom portion 25 b of the casing 25 is caulked to the opening end of the tubular portion 25 a. However, by fixing the bottom portion 25 b to the tubular portion 25 a in a detachable manner, manipulation of the spring force adjustment screw 37 may be allowed even after the bottom portion 25 b is fixed to the tubular portion 25 a.

The second stator 31 has a tubular shape. The opening end of the second stator 31 in the first stator 30 side is formed in a tapered shape such that its diameter is reduced toward the first stator 30 side. As a result, a magnetic flux generated when the electric current flows to the coil 28 concentrates on the right-end inner circumference side of the second stator 31. The shape of the left end of FIG. 1 of the nonmagnetic ring 32 interposed between the first and second stators 30 and 31 matches the shape of the tapered end of the second stator 31.

In the solenoid Sol, a magnetic path is formed by the first and second stators 30 and 31, and the rotor 33. As the coil 28 is magnetically excited, the rotor 33 neighboring to the first stator 30 is attracted to the second stator 31 side, so that a thrust force is applied to the rotor 33 toward the left side of FIG. 1.

The bottom of the rotor 33 abuts on the pilot valve body 38 of the pilot valve 6 such that the thrust force of the spring 36 is transmitted to the pilot valve body 38. When the solenoid Sol is magnetically excited, a thrust force directed to the left side of FIG. 1 is applied to the pilot valve body 38 by virtue of the attracted rotor 33. It is noted that, if the washer 34 is formed of synthetic resin or the like, it is possible to suppress impact or noise when the rotor 33 collides.

The pilot valve body 38 includes a large-diameter portion 38 a making sliding contact with the right-end inner circumference of the valve housing 22 in FIG. 1, and a cylindrical small-diameter portion 38 b extending from the left end of the large-diameter portion 38 a and facing the through-hole 22 c of the valve housing 22. The pilot valve body 38 is a flat valve for opening or closing the pilot passage 4 by seating or unseating the left-end outer circumference of the small-diameter portion 38 b of FIG. 1 on or from the pilot valve seat 22 a provided in the inner circumference of the valve housing 22. Since the small-diameter portion 38 b is spaced from the inner circumference of the valve housing 22, the pilot valve body 38 does not block the through-hole 22 c.

A spring 40 is interposed between the left end of the large-diameter portion 38 a of the pilot valve body 38 and the outer circumferential side of the pilot valve seat 22 a of the valve housing 22. The spring 40 exerts a thrust force such that the pilot valve body 38 retreats from the pilot valve seat 22 a so as to maximize the flow area of the pilot passage 4.

The pilot valve body 38 is interposed between the springs 36 and 40 through the rotor 33. A thrust force is applied to the pilot valve body 38 from the spring 40 so as to maximize the flow area of the pilot passage 4. In addition, a thrust force is applied through the rotor 33 from the spring 36 so as to reduce the flow area of the pilot passage 4.

While no electric current flows to the coil 28 of the solenoid Sol, the thrust force of the spring 40 is equal to or stronger than that of the spring 36, and the rotor 33 is forcibly inserted into the first stator 30 until the rotor 33 abuts on the washer 34. As a result, the pilot valve body 38 retreats from the pilot valve seat 22 a to the position where the flow area of the pilot passage 4 is maximized. While an electric current flows to the coil 28 of the solenoid Sol, the rotor 33 is attracted, so that the pilot valve body 38 is seated on the pilot valve seat 22 a resisting to the biasing force of the spring 40. That is, by adjusting the electric current amount flowing to the solenoid Sol, it is possible to adjust the thrust force applied to the pilot valve body 38 and control the valve opening pressure of the pilot valve 6.

The pilot valve 6 includes a pilot valve seat 22 a, a pilot valve body 38 seated on or unseated from the pilot valve seat 22 a, and springs 36 and 40 that interpose the pilot valve body 38. The pilot valve 6 is provided downstream from a portion where the penetrating hole 21 d and the cavity 21 c intersect, which is the connection point where the back-pressure chamber P of the pilot passage 4 is connected.

Since the springs 40 and 36 are arranged in series, it is possible to change a compression length of the spring 40 as well as a compression length of the spring 36, which is the length in a compressed state, by adjusting the support position of the spring 36 using the spring force adjustment screw 37. That is, it is possible to adjust initial loads of the springs 36 and 40 applied to the pilot valve body 38. By adjusting the initial loads, it is possible to adjust the valve opening pressure of the pilot valve 6 against the electric current amount supplied to the solenoid Sol. For the adjustment of the initial loads, any configuration other than the spring force adjustment screw 37 may also be employed if it can adjust the support position of the spring 36 in the axial direction.

The second stator 31 of the solenoid Sol protrudes to the left side in FIG. 1 from the solenoid bobbin 29. A spacer 35 is fitted to the left-end outer circumference of the second stator 31. The spacer 35 has a tubular shape and has a flange 35 a in the right-end inner circumference. The inner circumference of the flange 35 a is fitted to the outer circumference of the second stator 31. The spacer 35 is also fitted to the inner circumference of the tube 18 b provided in the outer tube 18. A gap between the spacer 35 and the tube 18 b is sealed with a seal ring 41 mounted to the outer circumference of the spacer 35.

The failsafe valve 26 includes a failsafe valve body 42 slidably mounted to the outer circumference of the sliding contact portion 22 d of the valve housing 22 and a spring 43 interposed between the failsafe valve body 42 and the flange 35 a of the spacer 35.

The failsafe valve body 42 having a tubular shape includes a brim 42 a provided in the outer circumference side, an annular protrusion 42 b facing the right-end face of the flange 22 b of the valve housing 22 in FIG. 1, an orifice passage 42 c that causes the inner and outer circumferences of the failsafe valve body 42 to communicate with each other, and a communication hole 42 d that is opened from the right end of FIG. 1 and communicates with the orifice passage 42 c. A spring 43 is interposed between the brim 42 a and the flange 35 a of the spacer 35, so that the failsafe valve body 42 receives a thrust force exerted toward the flange 22 b side of the valve housing 22 from the spring 43 at all times.

The right end of the failsafe valve body 42 faces the left end of the second stator 31, and a magnetic path is formed by the second stator 31, the failsafe valve body 42, the valve housing 22, the tube 18 b, and the casing 25. As described above, as the coil 28 is magnetically excited, the failsafe valve body 42 is attracted to the second stator 31, so that a thrust force is exerted to the failsafe valve body 42 toward the right side of FIG. 1. If the electric current supplied to the solenoid Sol exceeds a predetermined value I1, the thrust force applied to the failsafe valve body 42 from the solenoid Sol exceeds the thrust force of the spring 43. As a result, the failsafe valve body 42 abuts on the second stator 31, and the pilot passage 4 is fully opened.

If the electric current supplied to the solenoid Sol is equal to or lower than the predetermined value I1, the thrust force applied to the failsafe valve body 42 from the solenoid Sol is weaker than the thrust force of the spring 43. As a result, the failsafe valve body 42 moves to a failure position where the annular protrusion 42 b abuts on the flange 22 b of the valve housing 22 so that the flow area of the pilot passage 4 is restricted. In the failure position, the orifice passage 42 c of the failsafe valve body 42 faces the pilot passage 4, so that the pilot passage 4 communicates only via the orifice passage 42 c. Therefore, the flow area of the pilot passage 4 is restricted by the flow area of the orifice passage 42 c.

Therefore, if the electric current supplied to the solenoid Sol exceeds the predetermined value I1, the failsafe valve 26 moves to an open position where the pilot passage 4 is opened. If the electric current supplied to the solenoid Sol is equal to or lower than the predetermined value I1, the failsafe valve 26 moves to the failure position where the pilot passage 4 communicates only via the orifice passage 42 c.

It is noted that the communication hole 42 d is not blocked by the end portion of the second stator 31 and remains in the communication state even when the failsafe valve body 42 abuts on the second stator 31. In addition, even when the failsafe valve body 42 abuts on the second stator 31, the space where the rotor 33 is housed is not blocked. As a result, the pilot valve body 38 is not locked, and its movement is not prohibited.

As illustrated in FIG. 4, during a normal operation in which the electric current can be supplied to the solenoid Sol, the electric current is supplied to the solenoid Sol ranging from the electric current value I2 higher than the predetermined value I1 to the electric current value I3. During a failure, the electric current supplied to the solenoid Sol stops. When the electric current ranging from the electric current value I2 to the electric current value I3 is supplied to the solenoid Sol, the pilot valve body 38 of the pilot valve 6 is pressed to the pilot valve seat 22 a resisting to the biasing force of the spring 40 by virtue of the thrust force of the solenoid Sol and the biasing force of the spring 36.

When the pressure of the upstream side of the pilot passage 4 is applied to the pilot valve body 38, and a resultant force between the force of unseating the pilot valve body 38 from the pilot valve seat 22 a and the biasing force of the spring 40 exceeds a resultant force between the thrust force of the solenoid Sol and the biasing force of the spring 36, the pilot valve 6 is opened, so that the pilot passage 4 is opened accordingly. That is, when the pressure of the upstream side of the pilot passage 4 reaches the valve opening pressure, the pilot valve 6 is opened, so that the pilot passage 4 is opened accordingly.

In this manner, when the electric current ranging from the electric current value I2 to the electric current value I3 higher than the predetermined value I1 is supplied to the solenoid Sol, it is possible to adjust the valve opening pressure of the pilot valve 6 by adjusting the thrust force of the solenoid Sol based on the amount of the electric current. As the pilot valve 6 is opened, the pressure of the pilot passage 4 upstream from the pilot valve 6 becomes equal to the valve opening pressure of the pilot valve 6. Therefore, the pressure of the back-pressure chamber P is also controlled by the valve opening pressure.

As described above, when the solenoid valve V is operated normally, the electric current ranging between the electric current values I2 and I3 higher than the predetermined value I1 is supplied to the solenoid Sol. As a result, the valve opening pressure of the pilot valve 6 is controlled, and the failsafe valve 26 causes the pilot passage 4 to remain in the opened state.

In comparison, during a failure in which supply of the electric current is naturally prohibited, the electric current is not supplied to the solenoid Sol even when the electric current can be supplied. In addition, the upper limitation I3 of the electric current value for a normal operation is defined by the specification of the solenoid Sol. The lower limitation of the electric current value for a normal operation is set to the electric current value I2 higher than the predetermined value I1 where the failsafe valve 26 switches to the failure position. Such a setting is to prevent the failsafe valve 26 from switching to the failure position when a normal operation is desired due to a change of the electric current supplied to the solenoid Sol or a shortage of the electric current caused by fluctuation of a power voltage or noise. Therefore, a margin is provided between the predetermined value I1 and the lower limitation I2 of the electric current value for a normal operation such that an erroneous operation can be prevented.

Next, a description will be made for operation of the solenoid valve V.

When the solenoid valve V is normally operated, the electric current ranging from the electric current value I2 to the electric current value I3 is supplied to the solenoid Sol, so that the valve opening pressure of the pilot valve 6 is adjusted. As a result, a pressure of the pilot passage 4 between the orifice 5 and the pilot valve 6 is guided to the back-pressure chamber P via the communication passage Pr.

In this manner, it is possible to adjust the internal pressure of the back-pressure chamber P and the pressure applied to the rear face of the leaf valve 3 by adjusting the valve opening pressure of the pilot valve 6. Therefore, it is possible to control the valve opening pressure for opening the main flow passage 1 of the main valve M.

That is, the valve opening pressure in the main valve M including the leaf valve 3 and the valve seat 2 is adjusted by the electric current amount supplied to the solenoid Sol. When the shock absorber D expands, the internal pressure of the rod-side chamber 13 can be controlled to the valve opening pressure of the main valve M. When the shock absorber D contracts, the internal pressure of the cylinder 10 can be controlled to the valve opening pressure of the main valve M.

When the electric current supplied to the solenoid Sol is set to the electric current value I2, the valve opening pressure of the pilot valve 6 is minimized, and the valve opening pressure of the main valve M is also minimized. In this case, the shock absorber D generates a minimum soft damping force. On the contrary, when the electric current supplied to the solenoid Sol is set to the electric current value I3, the valve opening pressure of the pilot valve 6 is maximized, so that the valve opening pressure of the main valve M is maximized. In this case, the shock absorber D generates a maximum hard damping force. As a result, it is possible to adjust the damping force of the shock absorber D steplessly from the soft level to the hard level by changing the electric current amount supplied to the solenoid Sol.

In the solenoid valve V, there is a time difference between a valve opening timing of the main valve M and a valve opening timing of the pilot valve 6, so that the valve opening timing of the main valve M is delayed from the valve opening timing of the pilot valve 6. That is, the main valve M is not opened by the pressure of the rod-side chamber 13 when the pilot valve 6 reaches the valve opening pressure. The valve opening pressure of the main valve M is set to exceed the pressure of the rod-side chamber 13 necessary to open the pilot valve 6.

The rear face-side pressure receiving area Ah of the leaf valve 3 is set to be larger than the front face-side pressure receiving area As. The ratio therebetween is set to “As:Ah=1:1.5.” That is, the rear face-side pressure receiving area Ah is set to 1.5 times the front face-side pressure receiving area As. As a result, even when the pressure of the upstream side of the pilot passage 4 reaches the valve opening pressure of the pilot valve 6 by virtue of the pressure of the rod-side chamber 13, the internal pressure of the rod-side chamber 13 at that time does not reach the valve opening pressure of the main valve M, and the main valve M is not opened.

It is noted that the ratio between the front face-side pressure receiving area As and the rear face-side pressure receiving area Ah may be set to any other ratio without limiting to “As:Ah=1:1.5” if the internal pressure of the rod-side chamber 13 does not reach the valve opening pressure of the main valve M when the pressure of the upstream side of the pilot passage 4 reaches the valve opening pressure of the pilot valve 6 by receiving the pressure of the rod-side chamber 13. By satisfying the aforementioned condition, it is possible to set the ratio between the front face-side pressure receiving area As and the rear face-side pressure receiving area Ah so as to generate a time difference between the valve opening timing of the main valve M and the valve opening timing of the pilot valve 6 and delay the valve opening timing of the main valve M from the valve opening timing of the pilot valve 6. In addition, by changing the biasing force of the spring 27 for biasing the main spool 23, it is possible to change a relationship between the front face-side pressure receiving area As and the rear face-side pressure receiving area Ah to satisfy the aforementioned condition.

In this manner, in the solenoid valve V, the main valve M is not opened when the pilot valve 6 is opened. Therefore, it is possible to suppress influence on the valve opening of the main valve M even when a response delay is generated in the event of valve opening of the pilot valve 6. Therefore, it is possible to prevent an abrupt change of the damping force generated by the shock absorber D.

If the solenoid valve V is used in the shock absorber D in this manner, it is possible to suppress vibration or abnormal noise in a chassis. Therefore, it is possible to improve a vehicle ride quality without making passengers feel discomfort.

Furthermore, the right-end face of FIG. 1, which is the contact surface of the valve seat 2 where the leaf valve 3 is seated or unseated, is roughened. As a result, it is possible to prevent the leaf valve 3 from adhering to the valve seat 2 and make the leaf valve 3 easy to open. Therefore, it is possible to alleviate the delay of the valve open timing of the main valve M and further alleviate an abrupt change of the damping force of the shock absorber D.

Moreover, using the solenoid valve V, it is possible to control the internal pressure of the back-pressure chamber P and adjust the valve opening pressure of the main valve M by applying the thrust force corresponding to the electric current supplied to the solenoid Sol to the pilot valve 6. As a result, it is possible to adjust the internal pressure of the back-pressure chamber P to a desired value without depending on the flow rate of the pilot passage 4. Even when the expanding or contracting rate of the shock absorber D is at a low rate area, it is possible to nearly linearly change the damping force against the electric current supplied to the solenoid Sol and improve controllability. In addition, since the internal pressure of the back-pressure chamber P applied to the rear face of the leaf valve 3 is controlled by applying the thrust force to the pilot valve 6 depending on the electric current supplied to the solenoid Sol, it is possible to reduce a deviation of the damping force.

Since no electric current flows to the solenoid Sol during a failure, the pilot valve 6 opens the pilot passage 4, and the failsafe valve 26 restricts the flow area of the pilot passage 4 to the flow area of the orifice passage 42 c.

As the shock absorber D is operated to expand or contract in this state, the internal pressure of the back-pressure chamber P is defined by resistances of the orifice 5 and the orifice passage 42 c. As a result, it is possible to set a characteristic of the internal pressure of the back-pressure chamber P against the expansion or contraction rate of the shock absorber D in the event of a failure in advance and set the valve opening pressure of the main valve M to an arbitrary value.

During a normal operation, as the damping force of the shock absorber D is adjusted by adjusting the valve opening pressure of the main valve M, the failsafe valve 26 is in the open position, and only the pilot valve 6 is operated. Therefore, it is possible to independently adjust the valve opening pressure of the pilot valve 6 by excluding influence of the failsafe valve 26. In addition, during a failure, the flow area is restricted only by the failsafe valve 26 without restricting the pilot passage 4 using the pilot valve 6.

Therefore, there is no influence on the failsafe valve 26 even when the initial loads of the springs 36 and 40 applying the thrust force to the pilot valve body 38 of the pilot valve 6 is adjusted in order to correct a deviation between products caused by their allowances and the like. Therefore, since there is no influence on the damping force in the event of a failure, it is possible to remove a deviation between products during both a failure and a normal operation.

Since the main valve body of the main valve M is a thin leaf valve 3, it is possible to prevent the sizes of the solenoid valve V from increasing in the axial direction. It is noted that other types of valve bodies such as a spool or a poppet valve may be employed as the main valve body without limiting to the leaf valve if it can adjust the valve opening pressure with the internal pressure of the back-pressure chamber P applied to the rear face of the main valve body.

Furthermore, since the failsafe valve 26 has the orifice passage 42 c that faces the pilot passage 4 to restrict the pilot passage 4 as it switches to the failure position, it is possible to simplify the structure of the solenoid valve V without necessity of arranging a subsidiary flow passage having a separate orifice in parallel in the pilot passage 4.

It is noted that, instead of the orifice passage 42 c, a subsidiary flow passage having an orifice may be provided in parallel with the pilot passage 4 such that the pilot passage 4 is perfectly blocked by the failsafe valve 26, and only the subsidiary flow passage works in the event of a failure.

Other types of valves such as a choke valve may also be employed to restrict the flow area of the pilot passage 4 in the failsafe valve 26 instead of the orifice passage 42 c.

The failsafe valve 26 may be omitted. In addition, other types of solenoids Sol can be employed without limiting to the configuration, the structure, and the magnetic path described above if it can drive the pilot valve 6.

Embodiments of the present invention were described above, but the above embodiments are merely examples of applications of the present invention, and the technical scope of the present invention is not limited to the specific constitutions of the above embodiments.

This application claims priority based on Japanese Patent Application No. 2013-027394 filed with the Japan Patent Office on Feb. 15, 2013, the entire contents of which are incorporated into this specification. 

1. A solenoid valve comprising: a main valve having a valve seat provided in a main flow passage, and a main valve body seated on or unseated from the valve seat to open or close the main flow passage; a pilot passage that branches from the main flow passage; an orifice provided in the pilot passage; a back-pressure chamber connected to the pilot passage downstream from the orifice, the back-pressure chamber being configured to bias the main valve body to a closing direction by virtue of an internal pressure; a pilot valve disposed in the pilot passage downstream from a connection point to the back-pressure chamber, the pilot valve being configured to control an internal pressure of the back-pressure chamber; and a solenoid configured to control a valve opening pressure of the pilot valve, wherein there is a time difference between a valve opening timing of the main valve and a valve opening timing of the pilot valve such that the valve opening timing of the main valve is delayed from the valve opening timing of the pilot valve.
 2. The solenoid valve according to claim 1, wherein the time difference between the valve opening timing of the main valve and the valve opening timing of the pilot valve is set by a ratio between a front face-side pressure receiving area where the main valve body receives a pressure of upstream of the main flow passage and a rear face-side pressure receiving area where the main valve body receives the internal pressure of the back-pressure chamber.
 3. The solenoid valve according to claim 2, wherein the valve seat has an annular shape, the main valve body is an annular leaf valve, the back-pressure chamber is defined by a main spool having a tubular shape, the main spool provided in a rear face side of the leaf valve, the main spool abutting on the rear face of the leaf valve, the front face-side pressure receiving area is set by a seat diameter of the valve seat, and the rear face-side pressure receiving area is set by an inner diameter of the main spool.
 4. The solenoid valve according to claim 1, wherein a contact surface of the valve seat where the main valve body is seated is roughened. 